1. Field of the Invention
The present invention relates to a heat-resistant nickel-base alloy having excellent high temperature strength and weldability.
2. Description of the Prior Art
With the recent technical progress in the nuclear reactors, a high temperature gas reactor has been developed, and demands have been made for development of a heat-resistant material which is stable for a long period at high temperatures above 700.degree. C. Thus, trials have been made for using the high temperature gas coming out of the gas reactor for power generation and heat treatment and heat-resistant alloys, such as, Cr-Ni-Ti-Fe alloys and Ni-Mo-Fe alloys have been used as materials for the heat transferring pipes and tubes. However, these conventional alloys can not maintain high strength in a stable manner for a long period at high temperatures above 900.degree. C.
The present inventors have made extensive studies for developing a heat-resistant alloy for welded structures, which shows stable high strength at high temperatures above 900.degree. C. and good weldability as well as excellent hot workability, and have made extensive experiments on various alloy compositions.
However, when heat-resistant alloys are used in the primary system of a high temperature gas nuclear reactor, a problem arises if the alloys contain cobalt since this cobalt is entangled into the oxide scale which is formed on the surface of the alloys under some circumstances, and this oxide scale peels off and is radiated within the reactor, and its induced radioactivity causes difficulties.